Hardenable epoxy resin compositions and process for making the same

ABSTRACT

A curable composition comprising a mixture of an epoxy resin and a hardener can be prepared by dissolving the resin and curing agent in a low boiling solvent and flashing off the solvent at temperatures in excess of 400*F, the evaporating solvent cooling the composition and minimizing precure of the resin. Reinforced composites can be prepared by passing a supporting material such as a continuous web strand or roving through the resin solution and thereafter heating at temperatures above 400*F to remove the solvent without appreciably precuring the resin. The curable epoxy compositions can be used for molding, laminating and the like.

United States Patent Flynn Aug. 26, 1975 HARDENABLE EPOXY RESIN 3,479.302 u/we Saran 26012 COMPOSITIONS AND PROCESS FOR 3,523,037 8/1970 Chellis 260/47 3,634,326 1/1972 Aubry 260/47 MAKING THE SAME Inventor: Robert Flynn, Toms River, NJ.

Assignee: Ciba-Geigy Corporation, Ardsley,

Filed: July 14, 1972 Appl. No.: 271,872

Related US. Application Data ROVING RATE FTJMIN.

Primary Examiner-Me1vin Goldstein Assistant Examiner-E. A. Nielsen Attorney, Agent, or Firm-Vincent J. Cavalieri; Nestor W. Shust [57] ABSTRACT A curable composition comprising a mixture of an epoxy resin and a hardener can be prepared by dissolving the resin and curing agent in a low boiling solvent and flashing off the solvent at temperatures in excess of 400F, the evaporating solvent cooling the composition and minimizing precure of the resin.

Reinforced composites can be prepared by passing a supporting material such as a continuous web strand or roving through the resin solution and thereafter heating at temperatures above 400F to remove the solvent without appreciably precuring the resin.

The curable epoxy compositions can be used for molding, laminating and the like.

5 Claims, 1 Drawing Figure C 200 300 40 F 692 572 T52 TOW E R TEM l HARDENABLE EPOXY RESIN COMPOSITIONS AND PROCESS FOR MAKING THE SAME CROSSREFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of US. Ser. No. 83,626, filed Oct. 23, I970 now US. Pat. No. 3,679,465, which issued on July 25, I972, which application is a continuation-in-part of U.S. Ser. No. 877,477, filed Nov. I7, 1969, and now abandoned.

BACKGROUND OF THE INVENTION The epoxy compositions with which this invention is concerned are thermosetting systems formulated to meet various processing techniques and applications requirements. They usually include the resin and the curing agent together with extenders or reinforcements. These latter materials are virtually indispensable in many applications; and were used, the problem the art faces is in providing the resin, the curing agent and the reinforcements together in a stable system which can subsequently be transformed into desired articles by curing in, for example, a compression or transfer molding process. A simple blending technique is not suitable, especially where reinforced articles are used because the reinforcement material must be used as relatively large particles to perform well. The presently available methods for producing curable reinforced resin compositions generally involve coating or impregnating the suitable reinforcement material with the resin and its curing agent. These techniques, however, suffer from one or more disadvantages which renders them unsuitable for producing compositions from highly reacted components such as epoxy materials.

DESCRIPTION OF THE PRIOR ART In the conventional methods employ ed, the elevated temperatures required during the process of coating or impregnating a support with a resin and curing agent are in the range of the temperatures used for actual molding and tend to cause the resin and the curing agent to react to an undesirable degree. While this reaction may be quite slow and relatively incomplete, depending on the particular materials used, in general the characteristics of the composition are so deleteriously affected that in many instances the final product is practically worthless.

In attempting to arrive at a suitable intermediate solid, tack free and which has good curing properties, the prior art has attempted a variety of techniques, For example, prior artisans have blended powdered curing agents with powdered epoxy resins. Alternatively, a solid epoxy has been melted, the curing agent added and the mixture cooled and pulverized.

Respecting the incorporation of fillers. the prior art has attempted the so-called hot melt process wherein the materials are meited at an elevated temperature and a reinforcement material blended into the hot melt.

The degree to which the material is coated by the resin and curing agent land thus the ultimate properties are the final composition) is in part a function of the systems viscosity. This in turn is a function of the melt characteristics of the resin and the curing system and the fabrication temperature used. Additionally, resins and curing agents having both low melting points and widely useful characteristics as linal products are not generally known. This particular method has drawbacks which render it unsuitable for making such materials as epoxy molding compounds.

Another technique involves the use of systems which are liquid per se, as liquid resins and curing agents as direct coatings on reinforcement material. This system, like the hot melt system, is not of broad use and. after coating, the epoxy system must be advanced, i.e. cured so as to yield a solid tack free composites at room temperature. This requires controlled curing in order to produce a uniform composite with attendant expenses of process control.

Yet another technique has involved the use of a solvent to reduce the viscosity of either liquid systems or to solubilize solid resin/curing agent systems with subsequent application of the resulting liquid to the reinforcement material. The technique, however, is at tended by considerable difficulties when applied to epoxy systems. Typically, this approach involves dis' solving the resin and curing agent in a solvent, applying this solution somehow to reinforcement materials, such as roving for example, and then removing the solvent to leave behind a resin/curing agent system. The major problem is in removing the solvent so as to leave a resin curing agent composition which will have desirable physical properties when molded. On the one hand, high temperature solvent removal causes the epoxy systems to advance or precure at a point in time when this is intolerable. On the other hand, low temperature solvent removal often results in rapid removal of the solvent from the surface of the coating while remaining solvent below the surface is prevented from evaporating by the solid skin that is formed. This is quite a serious problem in processes where the resin system is being applied continuously to filamentous or fibrous materials such as roving or gauze and the like. In any case compositions produced from such material often fail to have acceptable mechanical or electrical proper ties in one respect or another.

To date, the prior art has been unable to obtain a satisfactory dry, solid taclofree epoxy composite based on a solid resin and more particularly has been unable to obtain a dry, solid tackfree reinforced composite having the combination of a. good flow characteristics,

b. rapid curing and,

c. low solvent level.

The prior art has thus employed a variety of methods to obtain composites having desired characteristics. The typical fabrication technique employed by the prior art is to dissolve either a highly functional solid resin or a liquid resin in a solvent, add a curing agent and impregnate or coat a desired substrate. Following the coating the solvent is removed at relatively low temperatures, typically 250 to 320F and thereafter the resin is advanced to the desired degree by exposure of temperatures of 300 to 350F. In this way, there is obtained a substantially advanced resin which, because it is already partially cured, cures relatively rapidly, This partially cured resin still has some flow although substantially less than the starting material because of the resin/curing agent advancement. This partially cured resin, of course, has a low solvent content. Ty pical of the prior art approaches to the problem are US. Pat. No. 3,523,037 and US. Pat. No. 3,480,47 I. These references generally teach that it is known to manufacture preimpregnated webs containing epoxy resin by first impregnating a supporting material used with an poxy resin solution containing a curing agent and iereafter evaporating the solvent by heat treatment. he resulting impregnated webs can thereafter be ressed with application of heat and pressure to form iminates. Where liquid epoxy resins are employed it is enerally desirable to obtain, after impregnation, a ontacky prepregv This is accomplished after the solent has been evaporated by exposing the impregnated 'eb for a certain period of time to a higher temperaire during which a portion of the curing agent reacts 'ith the epoxy resin and the latter is converted into a igher molecular, higher viscosity solid but still fusible prelengthened" state (the so-called B-stage),

It can be seen that in no case is the prior art able to btain a dry, solid, tack-free reinforced composite 'hich has the combination of good flow characteriscs, rapid curing. low solvent level and substantial re- :ntion of the original epoxy value.

SUMMARY OF THE INVENTION This invention relates to dry, solid, tack-free curable poxy resin compositions comprising an epoxy resin nd a curing agent, the composition characterized by solvent content below about (1.5% and a retained poxy value of at least 75%. In one aspect. the invenon relates to those systems wherein curable epoxy :sin compositions are applied to continuous reinforceient materials. One embodiment relates to the prepa- .ltion of chopped prepreg for molding. In another cmodiment the invention relates to impregnated filament ir filament winding. In yet another embodiment the ivention relates to impregnated web for laminating mother aspect of the invention relates to the preparaon of curable epoxy resin compositions. In one emodiment of this aspect of the invention an epoxy resin nd a curing agent therefor are dissolved in a low boilig solvent. a reinforcing substrate such as a web, [rand or roving is passed through the solution and the JIVCIII is thereafter flashed off at elevated tempera- .ires whereby the resin composition is evaporatively ooled and precure of the resin is minimized.

In another aspect of this invention a normally solid poxy resin and a curing agent therefor are dissolved in low boiling solvent and the resulting solution is dried t elevated temperature to recover a curable resin com osition characterized by a solvent content below bout 0.571 and a retained epoxy value of at least 757:. 1 one embodiment of this aspect of the invention the .)lution of epoxy and hardener is spray dried at eleated temperatures to yield a powdered curable comosition. In another embodiment of this aspect of the ivention the solution of epoxy resin and hardener is ietered onto an impervious support, such as a stainless Leel tape and exposed to elevated temperatures to dry ie composite. The resulting curable film or tape can e stripped intact from the support. Such films are usell per se. as adhesives and can be pulverized to form owdered resins. In yet another embodiment of this asect of the invention the solution of epoxy resin and ardener can be mixed with fillers and extenders. the :sulting composition metered onto an impervious suport such as a stainless steel tape and dried at elevated :mperatures. The resulting composition can be rcloved from the substrate and comminutcd to yield 'ansfer and compression molding compositions.

As can be seen from the above. an important step in re practice of the invention is the preparation of a solution of epoxy resin and a curing agent. The choice of solvent is. of course, significant to the concept that a low boiling solvent used in conjunction with a high energy rapid drying step will absorb most of the energy of the drying step as the solvent evaporates with very little, if any, energy being diverted to undesirable curing or B-staging of the epoxy resin. As a general proposition, the solvents suitable for use herein are those organic solvents which have a low boiling point at atmospheric temperature. By low boiling" is meant solvents boiling in the range of from about 30C to about 100C at atmospheric pressure and preferably, in the range of from about 4U to 80C. A wide variety of solvents in the indicated boiling range is available, as exemplified by the following table:

dicth lkctonc lll l .5

As a general proposition, the halogenated solvents are undesirable due to their toxicity at elevated tempera ture but, if this factor is acce table, the halogenated solvents boiling in the indicated range are operable. The alcohol solvents are undesirable because of the problem of potential reactivity between the alcoholic groups and the epoxide groups. The preferred group of solvents are the ketone solvents with acetone and methyl ethyl ketone being preferred and acetone being especially preferred.

In producing the epoxy resin solution described, virtually any epoxy resin normally employed in the production of cured products can be used successfully. The resin actually selected will depend upon the properties desired in the final product and, therefore, such selection is largely within the discretion of the user. Although the inventionis particularly useful in treating highly reactive resins, for example, those with several epoxide groups per molecule, there can also be successfully employed those epoxy compounds containing two or more epoxy groups. It is a particular advantage of this invention that the major part of the resin functionality is retained obviating the need for polyfunctional resins and making the ordinary and commonly available resins useful in the manufacture of curable epoxy compositions. Further. there can be used solid, liquid and mixtures of solid and liquid resins.

The resins can be aliphatic. cycloaliphatic, aromatic, heterocyclic and the like and may carry such inert substitucnts as chlorine and others well known and commonly encountered in the art. The resins can be monomers or polymers. and they can also contain either linkages and ester groups as well. There can be used virtu ally any epoxide produced from a polyhydric alcohol of phenol and an epihalohydrin. Typical of the epoxides that can be used successfully, are those produced from epichlorohydrin and a polyhydric phenol or alcohol such as resorcinol. catechol. 1.2.6-hexat1etriol. sorbitol. mannitol. pentaerythritol. trimethylolpropane and glycerol allyl ether. Similarly. polymeric materials con taining polyhydric hydroxyls such as appropriately substituted polyethers and polyesters can likewise be employed. For example. there may be employed vinyl cyclohexane dioxide. epoxidized mono-, diand triglycerbutadiene dioxide. l.4-bis( 2,3-epoxypropoxy] ben7ene. l.3-bis(2.3-epoxypropoxy)benzenc. 4.4 bisl ZJ-epoxypropoxy )diphenyl ether. l.8-bis( 2.3- epoxypropoxy) octane. l ,4-bis (ZJ-epoxypropoxy )cyclohexane. 4.4'-bis(Z-hydroxy3.4-epoxybutoxy) diphenyldimethylmethane. l.3-bis(4,5-epoxypentoxy)-5- chlorobenzene. l,4-bis( 3.4-epoxybutoxy )2- chlorocyclohexanc. diglycidyl thioether. diglyeidyl ether, ethylene glycol diglycidyl ether. resorcinol di glycidyl ether. l.15.fi-diepoxyhexane3. l.2.5.6 diepoxyhexane. and l.Z.3.4-tetra( 'l-hydroxy-S. 4-epoxybutoxyjhutane.

ides.

Particularly preferred are epoxides prepared from bisphcnoLA llZ-hisl l-hydroxyphenyllpropane) phenols or cresols and epichlorohydrin, Especially suitable as bisphenol Aepiehlorohydrin polyepoxide resins of the formula and epoxidi7ed -|oly(o-cresols) of the formula wherein u. a and I) are positive numbers and R repre sents chlorohydrins, glycols. polymeric ether linkages and the like,

The curing agents used to effect the ultimate cure of the resin are those normally employed in the art. They can be the conventional hardeners. accelerators of the like which produce polymeri/ation of a polyepoxide resin by reaction of the oxirane ring. Typically employed are primary and secondary amines. amides, polyaniines and polyamides phenols. novalacs and acid anhydrides. As suitable curing agents there may. for ex- (ill and m-xylylene diamine'. adducts of acrylonitrile or monoepoxides such as ethylene oxide or propylene oxide. to polyalkylene polyamines such as diethylenetriamine or triethylenetetramine; adducts from polyamines such as diethylenetriamine or triethylenetetramine in excess and polyepoxides such as bisphenol-A polyglycidyl ethers; ketimines. for example from acetone or methyl ethyl ketone and bis(paminophenyl)methane; adducts from monophenols or polyphenols and polyamines; polyamides. especially those from aliphatic polyamines such as diethylenetriamine or triethylenetetramine and dimerised or trimerised unsaturated fatty acids. such as dimerised linseed oil fatty acid (Versamid); polymeric polysulphide ("Thiokol); dicyandiamide. and anilineformaldlehyde resins; polyhydric phenols. for example resorcinol. 2.2-bis(4-hydroxyphenyl)propane or phenolformaldehyde resins; boron trifluoride and its complexes with organic compounds such as BF -ether complexes and BF;;-amine complexes. for example BF monoethylamine complex; acetoacetanilide-BF complex; phosphoric acid; triphenylphosphite; polybasic carboxylic acids and their anhydrices, for example phthalic anhydride. A -tetrahydrophthalic anhydride, hexahydrophthalic anhydride 4-methylhexahydrophthalic anhydride. 3.6 endomethylene [3 tetrahydrophthalic anhydride. methyl-3,6endomethylene A- tetrahydrophthalic anhydride (=methylnadicanhydride). 3.4.5.6.7,7-hexachlor-3.h endomethylene A tetrahydrophthalic anhydride. succinic anhydride. adipic anhydride. azelaic anhydride, sehacic anhydride, maleic anhydride. dodecenylsuccinic anhydride; pyromellitic acid dianhydride or mixtures of such anhydrides,

The curing agents can be used singularly or in combination of two or more. The amount used is not critical and will depend on the resin. the particular curing agent and the desired properties; a typical range is 80 to 150% of the stoichiometric amount although the actual amount may vary from this range depending upon the particular composition which is to be cured. For purposes of stoichiometric calculations. one epoxy group is considered to react with one reactive hydrogen.

Additionally. accelerators may be included in the system to increase the speed of reaction between the curing agent and the polyepoxide in its ultimate application. particularly when using polyhydroxides and polycarboxylic acid anhydrides as curing agents. Addition' ally. some accelerators may have a primary effect as a curing agent per se. Useful accelerators are. for example. tertiary amines. their salts or quaternary ammonium compounds. for example. 2.4.fi-trisldime thylaminomethylJphcnol. henzyldimethylamine. Z-ethyl-4-methyl-imidazolc, triamylammonium phenolate; alkali metal alcoholates such as. for example. sodium hexanetriolate. dicyandiamide (cyanoguanidine benyoguanamine, imidazole. isonialide. tetramethyl diamine. benlyl dimethylamine, metaphenolene diamine and N.N N'.N'-tetramethyll 3-butadiamine (TMBDA). The amount of accelerator is usually less than the amount of primary curing agent. As little as 3.1% ranging to the stoichiometric amount based on the weight of the polyepoxide, can be used to accelerlie the curing reaction to a practical rate. The actual amount of accelerator used, however, will depend upon ihe composition which is to be cured. One significant Advantage of this invention is that the epoxy hardener system can be sensitized by the addition of accelerators without undue prccure.

The solution of one or more epoxide resins together with one or more curing agents and/or accelerators can )e further mixed with usual modifiers such as reactive iiluents, extenders, fillers, pigments, dyestuffs, plasti- :isers, levelling agents, flame-retardant materials and nold release agents. As exemplary of extenders, reinorcing agents, fillers and pigments which can be em- )loyed in the mixtures are anthracite tar, bitumen, glass "ibers, boron fibers, carbon fibers, cellulose, polyethylrne powder, polypropylene powder, mica, asbestos, quartz powder, slate powder. chalk powder, sand, dolonitic materials including calcium, magnesium and zinc :arbonates, aluminum trihydrate, gypsum, antimony ;rioxide, bentones, silica aerogel, lithopone, barytes, Litanium dioxide, carbon black, graphite, iron oxide or netal powder such as aluminum powder or iron powler. The epoxy resin compositions can, if desired, be "lexibilized in a variety of ways. For example, the cross ink density of the cured resin can be reduced by preeacting some of the epoxy groups, hardener groups or 10th, Another method of flexibilizing the epoxy com- )ositions is to add long chain epoxy compounds.

In preparing the epoxy resin solution, the amount of .he resin system (such as resin, curing agent and other iolute materials) used in the solvent system can vary. t is convenient and preferred to use from 40 to 75 )arts by-weight of solvent and 25 to 60 parts by-weight if the resin and any associated curing materials. In pre- Jaring the epoxy resin solution, this concentration of .he solutes should be such as to provide a solution of :onveniently handled viscosity. It has been found that be above ranges are adequate for this purpose.

Virtually any reinforcement material amenable to :ontinuous flow through a bath solution and stable at ;he temperatures employed in the process can be used .uccessfully. There can be used materials such as glass, )oron, graphite, silicon, ceramic fibers. sapphire filartents, as well as such synthetic fibers as polyacryloni- :rile, polyamide polyester and polyvinylalcohol. These naterials can be used in the form of cloths, tapes, webs, 'ovings, etc.

The substrate is typically impregnated with a solution )f epoxy resin, accomplished most conveniently by :ontinuously passing the substrate through the epoxy 'esin solution at a speed sufficient to pick up on the .ubstrate the desired amount of solution. This speed. of :ourse, will vary with the reinforcement material used. he number of ends per strand and the number of filanents per end, the tension on the reinforcing substrate is it passes through the solution, the viscosity of the :poxy resin solution and similar factors normally en- :ountered by and apparent to those skilled in the art. (especting tension, it will be appreciated that the exensive coating on any material having closely packed ilaments and ends will depend to some extent on the autness of the strand as it passes through the resin soution. It has been found that the best results are obained in the ultimate compositions when from about 21) to tillr of the wc lu of the coated reinforcement material is constituted by the dry epoxy resin system coating. It will be appreciated by those skilled in the art that the amount of impregnation of the resin system (on a solid basis) applied on the reinforcement can be varied by altering a number of the process parameters such as those indicated above. In one aspect of the in vention, fiberglass roving containing 15 to 30 ends per strand and 2t)44()8 filaments per end will pick up a desired amount of resin material from the resin solution when moving at temperature-speed relationships indicated in FIG. I.

After the reinforcing substrate has been coated to the desired level, the now solvent-wet composite is dried at elevated temperature conditions to substantially completely remove the solvent and to leave behind the dry resin/curing agent solid system in a substantially unadvanced state. Alternatively, the solution of epoxide resin/curing agent and filler, if any, can be subjected to high energy drying per se, for example, spray drying at elevated temperature to substantially completely remove the solvent and to leave behind the resin/curing agent solid system in a virtually unadvanced state. It should be noted that by the practice of this invention it is possible to remove upward of 99% of the solvent without substantially advancing the cure of the resin, a proposition that could not be achieved heretofore, More specifically, by the practice of this invention there is obtained a curable composition which con prises a resin and hardener or resin, hardener and reinforcing substrate, said compositions being characterized by a solvent content below about 0.5% and the retained epoxy value of at least 75%. The percentage of solvent is based on the entire weight of the resin and substrate where applicable. In a normal atmospheric environment the upper temperature limitation of the system is governed by the auto-ignition point of the sol vent use. However, when a blanket of inert gas, such as nitrogen or carbon dioxide is used. still higher temperatures can successfully be employed. The rate of passage of the coated or impregnated substrate increases with increasing temperature, as is evidenced by FIG. 1. It goes without saying that it is most desirable to use the highest possible rate and although it is possible to achieve rates in excess of 50 feet per minute, it has been found convenient to adjust the temperature so as to permit a rate of from 5 to 50 feet per minute, more usually from about 20 to about 45 feet per minute.

The temperature range can vary from about 4()()F to the flash point of the solvent being used. More generally, the temperature range will be from about 4OUF to about 950F. As a general proposition. the higher the temperature, the faster is the production rate and. of course, is shorter the residence time. The combination of time and temperature should not be so great as to appreciably effect the curing of the resin, yet at the same time, these parameters should not be so low in magnitude as to result in incomplete solvent removal.

As indicated above, the factors of time and tcmperaturc are adjusted to yield the product having a solvent content below about (1.5% and having a retained epoxy value of at least 759?,

The temperatures normally employed are substan' tially in excess of subsequent molding temperatures and it is indeed surprising that such low precuring is obtained under these conditions. In fact, the present pro cess permits very high temperature exposure of the cur able system and results in less curing as experienced with any other technique. While for most holding applications. it is acceptable if there remains. after solvent removal. more than about 50% of the total epoxy groups originally available for curing. the practice of this invention readily and routinely affords resin compositions having it retained epoxy value in excess of 759?.

In one embodiment of practicing the invention. resin composition having at least 75% retained epoxy value can be routinely obtained using temperatures as low as 300F. preferably from about 400 to about 950F and most preferably from about 550 to about 850F and this especially preferably when acetone is used as the sole solvent.

As indicated. the characteristics of low solvent retention and higher retained epoxy value are a function of exposure time and temperature, with higher temperatures requiring shorter exposure times. It is preferred to use the highest temperature and shortest dwell time possible. It has been found. for example, that for a 6 foot heated column used as a drying tower it is possible to obtain reinforcement speed rates of from to 50 feet per minute. Similar considerations apply to spray dried material.

In some instances. when reinforced material is being employed. it is desirable to.divide the drying tower into several sections, three for example. and provide gradually reducing temperatures. Thus. for example, that portion of the tower first encountered by the coated material can be set at the appropriate temperature with subsequent decreases in the temperature of other sections depending upon desired results. In some cases it has been found convenient to direct forced air as a cooling medium onto the coated material as it leaves the drying column. It is also helpful in many cases to have a flow of air or nitrogen running through the column to aid in removal of the vaporized Solvent. It is an especially preferred embodiment of this invention to employ substantially isothermal conditions for drying. By substantially isothermal conditions is meant a differential of no more than 50 Fahrenheit between the temperature of the tower first encountered by the coated material and the temperature of the tower where the material exits. Isothermal conditions are preferred because it has been found possible to obtain maximum production rates by use thereof. This proposition is illustrated by FIG. I.

Following the drying step. the dried material is typically collected and. if desired. collected and chopped into small staples in a manner well known to form chopped prepreg or, in the case of impregnated tapes. the tapes collected and. if desired cut into convenient sizes or subsequent lamination. or in the case of an unsupported film. recovered as such or comminuted to form powders. Laminated compression and transfer molded articles can be subsequently prepared by known techni ues. As a result of the invention. the preparation of such articles is facilitated by the very desirable flow and handling properties of reinforced niaterial.

Physical properties of the final molded products made from epo\ preimpregnated chopped strand pre mixed molding compounds (chopped prepregs) are excellent. possessing flexible strengths in excess of 50.000 psi. tensile strength in excess of 22.000 psi. impact strength in excess of IR foot pounds per inch of notch and typical Barcol hardness above 60. Such epoxy impregnated chopped strand premixed molding compounds have a resin content of from 34 to 40%. a A to I inch fiber length. a bulk density below 0.35. a bulk factor below 1.5 and the capacity to be compression molded at pressures of 950 psi or less and are impregnated with an unpigmented epoxy resin. As previously indicated. pigments. colorants and other fillers can be used as desired.

The invention thus provides a method for handling epoxy systems heretofore considered to be too sensitive for the preparation of epoxy compositions. All this is achievable without sacrificing any of the normally desirable characteristics of molding compounds. Materials produced according to this invention can be compression molded using low mold close times at standard curing temperatures and lower mold pressures. The net result is to provide for faster cycles. a superior product and lower mold pressure.

The following examples are given to illustrate specific embodiments of the invention. In each example. unless otherwise indicated, the following procedure was used.

A fiberglass roving was continuously passed at room temperature through a bath of an epoxy resin solution containing an epoxy resin. a curing agent and other ingredients as indicated. at the designated speed and tension. The roving picked up resin solution from the bath and was directed out of the bath and into the bottom of a vertical six foot drying column. The column was divided into three 2 foot sections heated as indicated. The air intake to the tower is room temperature air so as to provide a temperature gradient through the tower. As the coated roving left the drying tower. it was cooled with forced air and introduced into a chopper where it was chopped into 0.5 inch staple lengths. The chopped material was then compression molded and gave items having the indicated properties.

EXAMPLE I Epoxy Resin Solution {40' solids) Aralditc 7065 Anilinc/formaldehyde" curing agent I200 grants I38 grants Reinforcement Material Fiberglass roving 30 end strand i104 filaments/end) Rotiitg Rate It/min. 7.0 III 20.0 Roving lension grams N00 800 K00 lower Tcnip.(.-bottom 290 3-40 440 I'ower Temp.(.-middlc 325 425 Tower Tcmp CJop I50 300 400 'ii \olatllcs remaining 0.. 0.3 0.3 t Resin Pickup 33.3 37.3 36 lJ 'Araltlile 7005 is .i liispheiiol A-Iype of cpioy resin prepared from epiclilorhydnn and has the lormula herciiialitnc prciiously set forth It ha an L'piny \iIlIlL .ncrage of II II e uimlents per I00 gram and is .nailahlc lrom (IRA orporatioii. Summit. New Jersey "(tiring ageiitan aniliueilonnaldelndc resin iniol ratio M0 :4! prepared by adding .i iii|\tu|'e ol (0N part or 7.0 lornniltlehy dc and mu part of .l': ll('l to Ills parts ot aniline preheated hi (101' During its addition the innitire ls agitated and the temperature IIILIIIILIIINIti at HIT After addition. llIL temperature is maintained at 0% until the forinaltlchyilc l\ cniiipletcly consumed (about I hoursi Iliercaltcr. 540 parts iii 50' sodnini litdrondc is .itldetL the aqueous layer separated and the resin \iaslicd ulli \\.itcr at IT tliilil the pH ot the .lsll \tatcr is 7 5 \olatile .iit then reminetl tinder \aicuuni to l ll( .it Ill IIIIII Hg I pun iiluc is deliiicd as the li'actional number ol'epo\ group per I00 gram ot IIlilIL'I'I-ll |'c\l\'tl and is di.-it.-rniiiicil by dissolving the |n.iti r|.i| iii a minimum amount or acetone :ltltllllg c|i/\l .tlCtiIlill imti are. whim." of hromo heuol blue dllll pota llIIIl iodide ltl'lllyjlllg to Iclltix teiiipcrattile auil lilriitiiig \\\th 0 liuliochloiic i kttl 'I'wo of the final products were molded into ASTM 'I'ypc I tensile bars at a molding temperature of 360 mold close time of 5 minutes with a 1 hour post cure at 300F and had the following properties:

5 drostatlc pressure) which constitutes an excellent ma- Ts'flsils *"s t 5? W terial for high pressure fluid flow. The tensile bar exhibi Elonganon at tailure 0.52 0.04 1 o ited at a tensile strength at 5 of 26,500 psi and a per cent elongation at failure of 0.72. Material produced in the same fashion as the above pmcedurc rewind] g using the Same furmuldtion hut Chung-mg mv-mg Speed o azole as an accelerator instead of the T MBDA. Per wv '7 e to I ft./mm. and the tension to 800 grams was molded Lemrebm An ASTM H l tuml into 2 inch 90 elbows, using conventional molding Speclmen was prepared descnhfid hove and Show" 7 x 0. equipment. The mold close time was about 4 minutes to posse htrength Ol r1400 C 4 l I 3 t a v I o t I 3 with a molding temperature range of 340380lusing Llmgmun sufirll 2 90 ellmws a clamp pressure of 2000 psi on a I4 inch ram and I700 molded undfir Condmons m those above (Cum 1 I I- psi core pressure on a 1% inch ram (around 4 minutes). Tempernum 360 F) Shfiwn to possess f The elbow had a hydrostatic burst pressure of 2460 t emge hydrostatic burst Pmssure 2580 i 533 P 7 EXAMPLE 3 It can be seen from the above results that the process 7 t r of the invention yields moldable compositions ot exem- 4) Procedure of Example 1 was g f plat), physical characteristics especiany Suitable for conditions and formulations as follows with the indihigh pressure fluid flow systems. It does so using a very Gated results: reactive epoxy resin/curing agent system. For example.

w :1 siabo 83 i the abt e cpoosy resin St lutu n gel n ut I76 l N hirmulunun A B C second at I72 C.

Arnldite 7065 I200 (100 0 ECN 1280" n 600 I200 Dic andiamidc 4X 72 9) EXAMPLE 2 Bcntyl dimcthylaminc I taccclcratorl (1.2 5.0 3.8 The procedure oI Example I is followed varying the 30 Water as 54 73 a a, f0 h indi Acetone I I660 [603.2 I53K formulation ind LUfldlllt ns a Ilo s tth t e Dmcthylfunmmulc m8 252 337 LIQIICLl I'CSUlIS. Solids content (calculated I -10 40 Roving tension gram 900-1000 400-1000 J00I000 Roving Rate fL/min. I05 I01! I00 16 Tower Tcmp.(.-Imtton 34-0 340 3-40 Tower TcmpFCI-middle 325 325 325 Formulation Tower Tcmp.(.-top 300 300 300 Resin pickup 30.7 36.5 35.0 Aralditc 7065 I200 grams /9 Volatiles remaining 0.4I 0.53 0 (wk Dic \andiamidc (hardener) 4X grams Tensile Strength pis N.N N' N'-tctr:nnl:tlt l-l.3-butndi:ttninc at 25C [AS'IM 'l' pe l) 15,600 22.500 l5 -t00 ('I'MBDAI (accelerator) 3 grams 4() 9i Elongation at Failure 0.6 0.h| 0,67 Acetone 1060 grams Water 36 1173mm "|('l\i I280 is an cptnidi/cd pol \locrc.soll rcsin hining the I'ornlula hcrcinahotc Dintctlt)lli rtttttl'nidc lbX grams tated and a melting point ot approsintnlcl t 0"(' It is available from ("MY Ruin'brCcmcl Mnlcriul Corporation. Summit. Ne .lcrsc Fibreglass roving l5 cnd strand 5 i ;"II"-"- f dzm Each of the above formulations produces suitable ovm' enslon grams 34 molded articles although C has lower tensile properties. TvmnC=middlB 335 The composition being produced solclv from a highly 30o f'azi mp 315 lunctional cpoxlde, offers improved chemical resistance and deflection temperature and is thus useful under a wide variety of conditions. The above materials were molded into u) a 2 inch. EXAMPL F 4 elbow at 360380F and 2000 psi compression pressure on a I4 inch ram and a I700 psi core pressure This example illustrates the use of different solvent on 1%inch ram, 1)) a standard ASTM Type I tensile bar systems.

Formulation A B Aralditc 70(15 (sec l\- ample II I200 rants I200 grams I200 grams Aniline/Forumldch dc curing agent tsce lztoimplc I| I38 IRS I38 AL'LlUllL' 1050 lsnS 1X05 Water 0 Zoo n |)iltILll1 \llt ltlilllllltlu 0 0 200 l'lhrcglttss mung 0 end 30 cod 30 end strands strands strands Roung Rate 4 It y'tltllt I l I I 8 III] Rmiog lcnslon grains lllll 000 000 limel lcinp ("bottom 340 140 340 loner lenip nnddlc 1 115 25 loner lentpc top 00 00 '1 olznilcs rclnalning 0 I I I 0. I Resin Pickup 3i 4 04 35.7

(cured at .0100 and I5 ton pressure until gelled. tolloued b 4 tons pressure until cured). at a mold close time of 5 minutes (post cure 2 hours at 300F). The elbow had an average burst value of 3030:202 psi thy The product obtained from the above procedure. after being cut into 0.5 inch staples. was molded into ASTM Type I tensile bars at a molding temperature of tain a product having the desired properties. the identical formulation was run at three different temperature ranges as follows:

\"arnish Formulation (trams Araldite 70(15 (See E\ample I I iZon Aniline/Formaldelntle (tiring Agent [See Example I 1 I33 Acetone ZUSH Fiberglass Ro\ing 3" end strand Fabrication Parameters I II [II No. of Ro\ings 4 4 4 Toner 'I'emperaturu (F) Top 200092) 3(101 S72) 4Uo1752 [Control setting) Middle 225(437) 325lol7) 4151797) Bottom 241x404 I 3401044 4401 82-1) Ronng 'l'ension. kg/rm ing l.() l.() 1.1) Roving Rate. ft/min (v.3 l-Hl 2-H) Staple Length. inches (1.5 ()5 Fabrication Test Results Retained Volatiles. 9? (LI 1 (Hi9 (HIS Binder Pickup. '4 33.24 h 3H1! Varnish Epoxy Value cq/lllll g. 1)..(15 (L205 (l.2ll5 Prcprcg Epoxy Value cq/llll) g. l), I no (L166 0.1m Retained Epoxy Content. '4 SH) 81.0 Vsn I'ltimate strength at 25C psi )1 Elongation at failure From the above it will be seen that the materials are eminently suited for pipe fittings applications. In addition. it will be appreciated that formulation A. using one acetone as the solvent. permits the use of somewhat higher roving rates through the varnish solution. This is of substantial economic benefit.

Material produced in accordance with formulation A above in routine production runs normally displays a retained epoxy content of from to percent. That is. such material is B staged only to the extent of l() to 25?! thus indicating an even lesser tendency to advance when compared to solvent systems containing higher boiling components. The degree of advancement is measured by determining epoxy value. The raw material epoxy value in formulation A is an average of 0. l 9 eg/IUU gm. binder and the epoxy value of the dried material is an average of ().l 7 eq./l()() gm binder-a rctention of 89%.

EXAMPLE 5 In order to determine the relationship between gradi ent tower temperature and roving rate necessary to ob The results of the above are graphically demonstrated in FIG. I and it can clearly be seen that the relationship between average temperature under gradient conditions and roving rate is most linear approximating dr/dt (1.0885 feet per minute per degree Centrigrade. Thus. for every C (ZITF) increase in average tower temperature. the roving rate increases approximately 8.85 feet per minute. As can be seen. low volatile retention level. together with high retained epoxy value. were obtained throughout the temperature and roving rate variations.

An additional observation should be made. It can be seen from the above example that as the roving rate is increased. the percent binder pick-up is increased. With a given roving rate. however. the binder pick-up remains constant and a uniform product is obtained. It is clear that. all things being equal. one way of increasing the binder level is to raise the roving rate. Although increased rate of substrate reduces the varnish dwell time which would tend toward a lower pick-up. this is overshadowed by a lower run off of the varnish during the drying so as to result in an effective increase in pick-up.

EXAMPLE 6 This example illustrates the proposition that the way in which the average tower temperature is arrived at is not critical, This example further illustrates the signifi cance of roving rate in obtaining a desired product.

Varnish Formulation Grams Araldite 7(Ih5 IZUU Aniline Formaldchydc (uring Agent L1H Acetone Z(IS(I Fiberglass Roting 3|) end strand Fabrication Parameters No. of Rinings l l l Tower Temperature. C tl'| Top tour 320] lot 320 I81)! 350 (Control setting) Middle lNSl 3oS M51365; lXUl 35h) Bottom 2oo .Wl Zillll 392 lsol 35m Roving l ension kgfirtn ing I l l. l l.|l Roung Rate. lt 'min o (7 Sit Staple Length. inches (l 5 (I 5 (I 5 Fabrication Test Results Retained Volatiles. '6 H17 (1 II (I I Binder Pickup, '4 3| (v 31 4 32.) \arn|shI1po\ \aluc egglltll g lLZIH 121M (I 2H4 Ireprcg ILNHt \aluc etpllllt g (HF-o (1 I74 ll.l7-l

'1 7h 5 X5 1 N5 3 Retained I po\ Value.

In this example. as in the previous examples, C air was injected into the tower. The tower control settings were as indicated. resulting in a gradient temperature air column.

It can be seen from the above that a prepreg having 5 ing rate is linear approximating dr/dt 0.15] feet per a retained epoxy value of 85.35? and a retained volaminute per degree Centigrade. Thus. for every lllllC tiles level oflLZl and 0.25% was obtained from a gradi- (212F) increase in the tower temperature. the roving ent temperature setting and a constant temperature setr te can be increased approximately l5 feet per min ting. respectively, at the identical process parameters. Ute, rhig represents an increase f some 71 Over h It can further be seen that at a roving rate of 6 feet per ll) rate (,htuilmme under gradient umdmunx mmutc Pmduct having P! Value of On the basis of the indicated data the following relan i x n i A 76.5 was obtained. indicating that at the temperam h between mmpemwres a mung rule was 65m P Y u rate of 6 feet P mmute was mu lished, based on a linear function having a slope of to afford optimum properties. 5

EXAMPLE 7 Tower Average Temperature T Rtfliflg Rate ft/inin In order to determine the relationship between isotoo "(i i thermal tower temperature and roving rate necessary I 5 1 to obtain the product having the desired properties. the identical formulation was run at a variety ofisothermal i E temperature ranges and roving rates as follows: .150 27.7 3110 29.2 370 3o 7 3x0 33.1 Varnish Formulation Grill8 25 390 33.8 4H0 3.53 Araldite 7065 lZUl) 410 353 AnNine/Formaldehyde Curing Agent UK 420 38.3 Acetone 2051) 430 39.8 Fiberglass Roving end strand 4-40 M3 450 42H 30 460 44A 470 45.9 In this example air at the bottom temperature was in- 47A jected into the tower. resulting in an essentially isothermal temperature air column.

TABLE 2 Rm ing Rate. feet/minute ltHl I10 14.0 17.0 l4.(l ixii 2|.o 24.1)

E Volatile Retention l).| l4 (LlSH (I. Hi2 0.733 0.077 (HHS (LZlll 0.272

'6 Binder Pickup 31M 35.83 mm 3'-J.l(l .Wlii 334 Ji-iiio 3x114 'l'ower Temp.

Top 34a 240 240 240 ion Jiio Bill) Jon "r 4m -l h4 404 464 573 573 572 572 BottonL Zhll 21in Zhl) :ho 325 .125 325 325 sun sou Sill) Silt) m7 m7 bl? til? A Epoxy Value Retention (Computer Results) 63.36 78.52 l(l5.7-t iii as i s. ll 74in slsii 89.97

Rming Rate. feet/minute lR tl ZHI Z-Ltl 2o}! loll 30.0 350 3M "1 \olatilc RL'lCIitilHt lLU S iii-is [H H.131 new iiiisn (LltW (mo-i "i Binder Pickup 39.84 37 75 39.44 3.\'.75 39.5: 4|.3l 44in 45.50

loner 'lenipm 'ia fit 3:5 335 3:5 335 371) 37a 37o 370 I" l 7 (i 7 (i l 7 (i l 7 698 (N8 1598 (J8 Bottom. t 345 345 345 345 SW FM! 390 1 11) "l 053 as} (153 as 734 734 734 .124

W; 1u\ \ialiie Retention l(onipiiti:r Rustill 44.3w 7: s: ms: $6.8, ss s 77.21 nu Ni ii. I!

From the above. and from H0. 1 where roving rate vs. isothermal temperature is graphically illustrated. it can clearly be seen that the relationship between average temperature under isothermal conditions and rovhi computing the slope. data outside the following parameters were discarded;

can be seen that the desirable bulk density is one that will provide the greatest weight per unit volume consis tent with free flow. Such materials have a bulk density 7; PWLUP of below about 0.20 and preferably below about 0.35.

ratio between density of the molding material and density of the final molded article. As a general proposition EXAMPLE 8 it is preferred that the bulk factor be below about 1.5

.. and r ferabl below abi t L20.

lhis etample illustrates the properties of epoxy prep 3 u it) The molding index or flow is a response to the mold impregnated chopped strand premixed molding coni- 4 I temperature and applied molding pressure. It is desirpounds as a function of the staple length in inches. 7 v

. t able to provide a reinlorced molding compound that lhe varnish ot Example 7 was employed to prepare x M will afford flow at molding temperatures under relaepox\ preimpregnated chopped strand premised mo y 2 g tively low molding pressures. The FIG. 950 PSI used in mg compounds having a binder level of 7.. K. v IS the Example is the lowest pressure afforded by this lhe following table summarizes the properties at the ASTM test method. Although the example employs various staple lengths. As used herein the term binder I f r t the Lh mk K lam mdiemg 950 PSI molding pressure, it is possible to compresion r so c L"t" L L g mold at pressures below the 950 PSI test minimum. An- TABl F 1 other benefit derived from these high flow characteristies at low pressure is transfer molding capability.

Staple Binder "1' length l.c\cl Bulk Hulk Spfir. Retained Flow EXAMPLE 9 Pi, s--

llii.) 1 1| Dciisit Fictor Molded Sobcnt S cc A n h s prep e ucco dmg o Example 7. no no s which formulation was modified to contain of loadflload load/load 7 M mil) 294/, 357 13mm Hm UM 950/29 ECN l 8() (see Example 5). This \dIfllSlt was used to 2 sum 3457mm 522 4 50 an 950 30 prepare epoxy preimpregnated Chopped strand pre- /4 3953 333i 4 l7 5 H7532 950/4? mixed molding Compounds having the binder levels iniii W54 BUMIRTI SAM/tits i an 0.38 95m ns dicated in the table below.

Staple Binder Bulk Bulk Sp.(ir. 7r Retained Flow Length (in) Level ("/1 Density gni/cm" Factor Molded Solvent psi/sec no "U load/load load/ load i 352. 2631333 7.37/ L94 (l.2l

5.82 a Zsxs gin/.357 7027 l as (MS l no/32 4.7a is MIKE 3577.435 Sii-i rsii (L22 950/ Bulk density was determined in accordance with From the above it can be seen that the molding propmethod C of ASTM standard D W954i). The results erties ofthe chopped prepreg are outstanding throughare reported before and after application of the test out a wide range of binder level. load. The bulk factor is similarly calculated according It can further be seen that staple length has a less sigto ASTM standard I) l 895-69. nificant effect on flow than does binder level. It should Flow corresponds to the molding index according to also be noted that flow increases as binder level in- ASTM designation D 737-67. The figure reported Cor creases.

responds to the minimum force in pounds per square Chopped prepregs should have a bulk density below inch required to close the mold together with the closabout 0.20 preferably below about (L35, bulk factor iiig time in seconds. below l.5. preferably below about l.2(l, a binder level The bulk density of a chopped prepreg is highly ig from 25 to 50%. preferably from 30 to 4092. a staple iiilicant in terms of its use and is of great significanc length of from /4 to one inch a retained solvent content to the final user. Bulk density represents weight per below 0.59? preferably below 0.25%. a retained epoxy unit volume and ilthe weight per unit volume is too value ul)()\ About f bl uhuvc go m 35 low. ie. the material has a high bulk. then it will not and the capacity of being nioldable at 950 psi.

1.'ll\ fill l in ild cavitx. Moldin i cvcles' will have to ink EXAMPLEH) clude a pretorm step llltll'l may be undcsira c in terms of ease and convenience of processing. In at 'lhis example illustrates the impregnation ofcoiitinu tempting to reduce the bulk density of the intermediate composites. composite free flow is Until] sacrificed. It

ous glass cloth which can be used to manufacture lami mites and which can be used in hand lay tip applications iralditc 7005 120.8 o/ iniline Formaldehyde ('uring agent 1K4 or icctonc 208.8 or H) lrasolc Red B 111 FM 1 gram (ilass cloth I528 ans-2%? (cut to 'vg inch \tidthl abrication Process l'lark Scliut-bcl lihcr (ilass (orp Has an cpo\ cumpalal lc finish 5 H The impregnated glass cloth was evaluated for lamiating application. This test included a determination fpercent binder flow in the impregnated cloth well s the molding of a copper clad board for peel strength. i laminate of four plys of 3% inch by 3% inch cloth ere molded at 500 psi pressure for ten minutes in a ress at 177C tlF). To obtain the percent of binder ow. a 3 inch diameter disc was punched from the ured laminate and checked for retained binder. Test :sults showed a 13.7% flow which is well within the inge of commercial laminating prepregs.

Nine plys of 3% inch by 6 inch glass laminate were repared with one side to receive a copper cladding. he composite was molded using three minutes kiss ell at 177C (350F) and psi then a ten minute cure I 177C (350F) and 500 psi. The composite was ooled at 66C l5llF) in the press under 500 psi and iereafter removed and allowed to cool to room temerature prior to determining peel strength. A inch .rip produced an average of 9.5 pounds pull at 2 iches per minute which amounts to 12.5 pounds per lch pull. This peel performance is well within the perarmancc levels of commercially available systems and emonstrates the applicability of the high temperature npregnation technique thereto.

The following method was used to determine the aoxy value of the composites.

3.0 grams (i413 grams) of epoxy composite are acirately weighed to 0.01 grams by difference into a .)(1mm Erlenmeyer flask. To this is added 25mm of ac- 5 :one and the mix is digested for It) minutes or until the :sin is dissolved as determined by visual inspection. 50mm of benzyl alcohol is added to the flask and the ask is assembled on a hot plate stirrer and brought to :flux while stirring vigorously. At this point 3.0 grams f potassium iodide dissolved in 5.0 grams of distilled ater are added together with 20 drops of indicatoe soition (U. 1 gram of bromphenol blue diluted to mm 1 N-propanol). Titration is thereafter begun with (1.5 ormal hydrochloric acid. Titration is continued until 1c reference color disappears for 1 minute with the adition of one drop of HCL. During titration the refer ncc color will slowly yield to a greenish or grayish hue and thereafter to a brown or yellow. indicating an excess of HCL: The excess reacts with Kl to form Hl which in turn adds to the epoxy groups. When the H1 adds the solution will slowly return to the reference color. One minute is deemed an acceptable albeit arbitrary time in order to reduce the time of the test. The calculation is made as follows:

ml. HCl X N NCl The results are approximately 3 to 5'7: below theoretical and an acceptable deviation from the mean value with or :2.()/r.

The volatile content of the compositions is determined by the difference in weight before and after evaporative heating.

The binder level of roving and glass laminate systems is determined by ignition at I3UOF and the difference in weight.

in addition to the preparation of impregnated substrates for molding and laminating use. the process of this invention can also be employed to form an unsupported epoxy resin film or tape. useful in adhesive and laminating applications. Thus, when a continuous steel tape is passed through a bath of the varnish described in Example 7, which can be modified by the addition of suitable plasticizing materials if desired, such as liquid epoxy resins and other flexibilizers. and thereafter passed through an elevated temperature environment as described under preferably isothermal conditions and the solvent flashed therefrom and the resulting film subsequently stripped from the tape. there is obtained an unsupported curable epoxy resin film which can be used to form laminates. For example, this film can be layered alternately with glass cloth and/or copper foil. pressed and cured to form a laminate.

Similarly, a varnish, filled or unfilled. can be used in the above process and comminuted so as to form a dry powder suitable for powder coating or transfer molding applications, or an impregnant for a suitable reinforcing substrate.

What 1 claim is:

I. A method for making an epoxy composition which comprises dissolving an 1 .2-epoxy resin containing two or more epoxy groups and a conventional curing agent therefor in a non-reactive solvent boiling at from 30 to about 100C and thereafter exposing the mixture to a temperature of from 400 to 50F to evaporate the solvent, the condition of temperature and time of exposure being so adjusted and controlled that the resulting composition has a retained solvent level below about (1.5%. and is substantially uncured.

2. A method according to claim I in which the epoxy resin is solid at room temperature.

3. A method according to claim 1 in which the mixture is spray dried.

4. A method according to claim I in which the mixture is coated onto an impervious support and dried at the high energy conditions to form a continuous film.

5. A method according to claim I in which the solution of resin and hardener additionally contains extenders and fillers. the resulting composition is coated onto an impervious support, dried at the high energy conditions and the resultant composition is comminuted to form a powder. 

1. A METHOD FOR MAKING AN EPOXY COMPOSITION WHICH COMPRISES DISSOLVING AN 1,2-EPOXY RESIN CONTAINING TWO OR MORE EPOXY GROUPS AND A CONVENTIONAL CURING AGENT THEREFOR IN A NON-REACTIVE SOLVENT BOILING AT FROM 30* TO ABOUT 100*C AND THEREAFTER EXPOSING THE MIXTURE TO A TEMPERATURE OF FROM 400* TO 950*F TO EVAPORATE THE SOLVENT, THE CONDITION OF TEMPERATURE AND TIME OF EXPOSURE BEING SO ADJUSTED AN CONTROLLED THAT THE RESULTING COMPOSITION HAS A RETAINED SOLVENT LEVEL BELOW ABOUT 0.5%, AND IS SUBSTANTIALLY UNCURED.
 2. A method according to claim 1 in which the epoxy resin is solid at room temperature.
 3. A method according to claim 1 in which the mixture is spray dried.
 4. A method according to claim 1 in which the mixture is coated onto an impervious support and dried at the high energy conditions to form a continuous film.
 5. A method according to claim 1 in which the solution of resin and hardener additionally contains extenders and fillers, the resulting composition is coated onto an impervious support, dried at the high energy conditions and the resultant composition is comminuted to form a powder. 